RESUMO
The components of receptor tyrosine kinase signaling complexes help to define the specificity of the effects of their activation. The Caenorhabditis elegans fibroblast growth factor receptor (FGFR), EGL-15, regulates a number of processes, including sex myoblast (SM) migration guidance and fluid homeostasis, both of which require a Grb2/Sos/Ras cassette of signaling components. Here we show that SEM-5/Grb2 can bind directly to EGL-15 to mediate SM chemoattraction. A yeast two-hybrid screen identified SEM-5 as able to interact with the carboxy-terminal domain (CTD) of EGL-15, a domain that is specifically required for SM chemoattraction. This interaction requires the SEM-5 SH2-binding motifs present in the CTD (Y(1009) and Y(1087)), and these sites are required for the CTD role of EGL-15 in SM chemoattraction. SEM-5, but not the SEM-5 binding sites located in the CTD, is required for the fluid homeostasis function of EGL-15, indicating that SEM-5 can link to EGL-15 through an alternative mechanism. The multi-substrate adaptor protein FRS2 serves to link vertebrate FGFRs to Grb2. In C. elegans, an FRS2-like gene, rog-1, functions upstream of a Ras/MAPK pathway for oocyte maturation but is not required for EGL-15 function. Thus, unlike the vertebrate FGFRs, which require the multi-substrate adaptor FRS2 to recruit Grb2, EGL-15 can recruit SEM-5/Grb2 directly.
Assuntos
Proteínas/metabolismo , Receptores de Fatores de Crescimento de Fibroblastos/metabolismo , Receptores de Fatores de Crescimento de Fibroblastos/fisiologia , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/fisiologia , Proteínas Adaptadoras de Transdução de Sinal , Animais , Sítios de Ligação/genética , Caenorhabditis elegans/genética , Caenorhabditis elegans/metabolismo , Movimento Celular/genética , Proteína Adaptadora GRB2/genética , Proteína Adaptadora GRB2/metabolismo , Proteína Adaptadora GRB2/farmacologia , Genes , Proteínas de Membrana , Ligação Proteica/genética , Proteínas/química , Proteínas/genética , Receptores Proteína Tirosina Quinases/genética , Receptores Proteína Tirosina Quinases/metabolismo , Receptores Proteína Tirosina Quinases/farmacologia , Receptores de Fatores de Crescimento de Fibroblastos/genética , Transdução de Sinais/genéticaRESUMO
The Caenorhabditis elegans FGF receptor, EGL-15, is alternatively-spliced to yield two major isoforms that differ in their extracellular domains. The EGL-15(5A) isoform is necessary for the gonadal chemoattraction of the migrating sex myoblasts (SMs), while the EGL-15(5B) isoform is required for viability. Here we show that 5A is predominantly expressed in the M lineage, which gives rise to the migrating SMs and their sex muscle descendants, while 5B is predominantly expressed in the hypodermis. Tissue-specific expression, however, explains only part of the functional differences between these two receptor isoforms. 5A can carry out the reciprocal essential function of 5B when expressed in the hypodermis, but 5B is incapable of carrying out SM chemoattraction. Our data, therefore, indicate that the structural differences in these two isoforms contribute to their functional differences. Two lines of evidence indicate that the 5B isoform also plays a role in SM migration, implicating it in the repulsion that is observed when the chemoattraction is compromised. Thus, structural differences in the extracellular domains of these two isoforms can specify either attraction to or repulsion from the gonad.
Assuntos
Proteínas de Caenorhabditis elegans/metabolismo , Caenorhabditis elegans/fisiologia , Quimiotaxia , Mioblastos/metabolismo , Receptores de Fatores de Crescimento de Fibroblastos/metabolismo , Animais , Animais Geneticamente Modificados , Caenorhabditis elegans/anatomia & histologia , Caenorhabditis elegans/citologia , Feminino , Gônadas/fisiologia , Masculino , Músculos/metabolismo , Especificidade de Órgãos , Isoformas de Proteínas/metabolismoRESUMO
Fibroblast growth factor (FGF) receptors trigger a wide variety of cellular responses as diverse as cell migration, cell proliferation and cell differentiation. However, the molecular basis of the specificity of these responses is not well understood. The C. elegans FGF receptor EGL-15 similarly mediates a number of different responses, including transducing a chemoattractive signal and mediating an essential function. Analysis of the migration-specific alleles of egl-15 has identified a novel EGL-15 isoform that provides a molecular explanation for the different phenotypic effects of lesions at this locus. Alternative splicing yields two EGL-15 proteins containing different forms of a domain located within the extracellular region of the receptors immediately after the first IG domain. Neither of these two domain forms is found in any other FGF receptor. We have tested the roles of these EGL-15 receptor isoforms and their two FGF ligands for their signaling specificity. Our analyses demonstrate different physiological functions for the two receptor variants. EGL-15(5A) is required for the response to the FGF chemoattractant that guides the migrating sex myoblasts to their final positions. By contrast, EGL-15(5B) is both necessary and sufficient to elicit the essential function mediated by this receptor.
